Isopropyl benzene is an important raw material for organic chemical industries, which is a main intermediate compound of producing phenol, acetone and alpha-methyl styrene. In industry, isopropyl benzene is prepared by alkylation of benzene with propylene, with a main by-product of polyisopropyl benzene. As early as 1945, UOP discloses a process for preparing isopropyl benzene by a reaction of propylene and benzene in the presence of a solid phosphoric acidic catalyst (SPA process) (U.S. Pat. No. 2,382,318). The SPA catalyst can't catalyze transalkylation of polyisopropyl benzene, thus, the SPA process can only be operated at a high molar ratio of benzene-to-olefin (5˜7), and the yield of isopropyl benzene is only about 95%. In the 1980s, the Monsanto Company developed a process for producing isopropyl benzene using AlCl3 as the alkylation catalyst, which had been practiced in industry. AlCl3 cannot catalyze the transalkylation, thus the yield of isopropyl benzene of the AlCl3 process for isopropyl benzene is still relatively low, while the problems of serious pollution and corrosion of the devices are present.
In the 1990s, the companies of Dow, CD Tech, Mobil-Badger, Enichem and UOP and so on (U.S. Pat. No. 4,992,606, U.S. Pat. No. 5,362,697, U.S. Pat. No. 5,453,554, U.S. Pat. No. 5,522,984, U.S. Pat. No. 5,672,799, U.S. Pat. No. 6,162,416, U.S. Pat. No. 6,051,521) disclose in succession fixed bed processes capable of conducting transalkylation with a microporous zeolite as the catalyst. In the present art, alkylation of benzene with propylene is carried out in an alkylation reactor. The polyisopropyl benzene generated from the alkylation process is separated by distillation system, mixed with benzene and then fed into an transalkylation reactor with a single catalyst bed for transalkylation.
In the transalkylation of polyisopropyl benzene with benzene, the molar ratio of benzene to polyisopropyl benzene, the space velocity of the raw materials, and the composition of the polyisopropyl benzene will affect significantly the conversion of the polyisopropyl benzene and the amount of the impurity of n-propyl benzene. Normally, the transalkylation of polyisopropyl benzene produces more amounts of the impurity of n-propyl benzene, which reduces the quality of the product isopropyl benzene significantly. Therefore, increasing the conversion of the polyisopropyl benzene and reducing the amount of n-propyl benzene generated from the transalkylation by optimizing the process is of significant importance for increasing the production efficiency and improving the quality of products.